Fixed KisToolTransform not to create full-sized QImage copies of the node

Now the size of the QImage is limited by 3000px. If it is less,
the 3000px thumb is upscaled on the fly using QPainter.

There are several things left to be done:

1) Prescale the QImage to the flake size when the scale < 1.0
   (this is a regression of this patch
2) Try to remove all these non-centralized calculations and
   numerous member variables. As much as possible should be done with
   a simple QTransform.

CCBUG:263170